1. Field of the Invention
The present invention relates to digital output pressure sensors using a vibrating beam as a sensing element.
2. Prior Art
In the prior art, various sensors which use vibrating beams have been advanced. Usually some type of digital pulse is provided to indicate the force or pressure derived force on the beam. Some of the sensors utilize piezoelectric sensing, such as U.S. Pat. Nos. 3,470,400 and 3,479,536. A type of pivoting beam that is constrained in its path of movement is also shown in U.S. Pat. No. 3,649,857.
An additional patent relating to vibrating beams is U.S. Pat. No. 3,664,237 which is of general interest. Capacitance sensing of vibrating beams is illustrated in U.S. Pat. Nos. 3,187,579 and 3,762,223. In both of these patents the sensing capacitor plate is on the opposite side of a member from the drive coil.
A piezoelectric beam which flexes transversely because of accelerations in the mass at the end of the beam, or because of impact of micro meteroids is shown in U.S. Pat. No. 3,304,773. An accelerometer using a vibrating beam with capacitance sensing is shown in U.S. Pat. No. 3,505,866.
U.S. Pat. No. 4,149,422 issued Apr. 17, 1979 shows a vibratory wire pressure sensor which discloses a thin wire that is held under a spring load to create a pretension, and is loaded by pressure so that the natural frequency of the wire changes. The lever which is utilized to load the vibrating wire is mounted with a cross flexure connection that permits relatively free pivotal movement. For sensing, a current from an oscillator is passed through the wire and this current reacts with a magnetic field from a permanent magnet thereby causing the wire to move. This produces a back EMF and positive feedback at the current generating oscillator circuit sustains the vibration of the wire. Thus the sensor disclosed in U.S. Pat. No. 4,149,422 does not utilize capacitive type sensing.